The CCNet resource pack includes custom armour textures that can be activated by renaming armour items in a certain way.
To see these textures, you need to install Optifine or the CITResewn mod for Fabric.
Americanfor the USA
Austrofor the Austro-Hungarian Empire
Germanfor the German Empire
Ottomanfor the Ottoman Empire
Russianfor the Russian Empire
Italianfor the Kingdom of Italy
You can change the texture of leather horse armour by dyeing it a specific colour. Unlike player armour, this does not require Optifine or CITResewn - the CCNet resource pack itself is sufficient.